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# M17-15

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Math Expert
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

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16 Sep 2014, 01:01
00:00

Difficulty:

5% (low)

Question Stats:

95% (00:21) correct 5% (00:16) wrong based on 174 sessions

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Which of the following is not a divisor of $$42*36$$?

A. 12
B. 18
C. 21
D. 28
E. 49
[Reveal] Spoiler: OA

_________________

Kudos [?]: 132827 [0], given: 12378

Math Expert
Joined: 02 Sep 2009
Posts: 42269

Kudos [?]: 132827 [0], given: 12378

### Show Tags

16 Sep 2014, 01:01
Official Solution:

Which of the following is not a divisor of $$42*36$$?

A. 12
B. 18
C. 21
D. 28
E. 49

$$42*36 = 6*7*6*6 = 2*2*2*3*3*3*7$$. This number is not divisible by $$7^2 = 49$$.

_________________

Kudos [?]: 132827 [0], given: 12378

Intern
Joined: 16 Jul 2017
Posts: 34

Kudos [?]: 3 [0], given: 9

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07 Nov 2017, 12:19
Break 42 * 36 down into prime numbers --> 42 * 36 = (7)(3)(2) * (3)(3)(2)(2) or (7^1)(3^3)(2^3)
Now we need to check the answers to see if there are any prime factorisations that don't match up with the above.

A. 12 = (3)(2)(2) -- this is OK
B. 18 = (3)(3)(2) -- this is OK
C. 21 = (7)(3) -- this is OK
D. 28 = (7)(2)(2) -- this is OK
E. 49 = (7)(7) -- not OK! The original prime factorisation only has one 7, therefore this is NOT a divisor!

Kudos [?]: 3 [0], given: 9

Re: M17-15   [#permalink] 07 Nov 2017, 12:19
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# M17-15

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